Mechanism for providing emergency POTS service in event of loss of power to customer premises equipment for ISDN telephone lines

ABSTRACT

In order to ensure continuous telephone service to a customer premises served by an ISDN line, without requiring that the customer maintain an additional POTS line as an emergency back-up to the normally used ISDN service, ISDN signalling circuits and network termination interface components are modified, so that, in the event of a loss of power to customer premises digital communications equipment, a communication link between an auxiliary POTS telephone and the normal ISDN communication path to the central office may be established. There need not be any modification of the central office switch, per se, so that the integrity of the ISDN communication path with the central office line card remains unaffected. As a result, the central office equipment can continue to conduct standard ISDN communications with the customer premises equipment, even though the customer is employing a POTS back-up analog phone.

This is a continuation of application Ser. No. 08/500,189, filed Jul.10, 1995, now U.S. Pat. No. 5,943,404.

FIELD OF THE INVENTION

The present invention relates in general to telephone systems andnetworks, and is particularly directed to a new and improved mechanismthat is connectable with and may be integrated within transceiver cardand network termination interface components of an integrated servicesdigital network telephone system, for providing auxiliary, substitutetelephone service capability (plain old telephone service or POTS)between an auxiliary analog telephone installed at a customer premisessite and an integrated services digital network communication path(either extended or non-extended) to a line card of a central officeswitch, in the event of a power outage at the customer premises.

BACKGROUND OF THE INVENTION

Integrated services digital network (ISDN) communication systems enabletelephone service providers to supply multiple types of signallingchannels from a central office over a signal local loop twisted pair toa network termination interface at a customer premises site. FIG. 1diagrammatically illustrates a reduced complexity example of a typicalextended distance ISDN communication system, while FIG. 2diagrammatically illustrates a non-extended distance ISDN communicationsystem. The extended distance ISDN system of FIG. 1 is intended toenable a telephone service provider to supply multiple types ofsignalling channels from a central office (CO) site 10 over a PCM link(such as an optical fiber link) to a remotely located customer premisesequipment (CPE) site 20, while the non-extended network of FIG. 2provides a local loop directly from the central office to the customerpremises site. ISDN signalling channels typically include digital datachannels and/or digitized voice channels, as well as a separateadministrative channel that conveys call control information.

More particularly, in the extended distance system of FIG. 1, thecentral office site 10, which is located at a ‘west’ end of an extended(PCM) communication link 30, includes a central office switch 11 (suchas a 5ESS switch manufactured by AT&T), which contains a plurality ofline termination circuits (or line cards), one of which is shown at 12.For extended distance communications carried out by the system of FIG.1, line card 12 is coupled over a local loop (twisted tip/ring pair) 13to what is termed in the telephone industry as a U Basic Rate-OneTransmission Extension (U-BR1TE) transceiver card 14 (also known in theindustry as a Basic Rate Interface Transmission Extension (U-BRITE)card).

The U-BR1TE (or U-BRITE) card contains an ISDN transceiver unit and anassociated PCM bus interface which are operative to transmit and receivestandard 2B+D ISDN data traffic over a PCM digital data link, such as aT1=1.544 MB/s link, and to interface the ISDN signals via the local loopto and from loop termination equipment. Namely, the U-BR1TE card 14interfaces the local loop 13 with a digital data link 30 for PCMcommunications transport to another U-BR1TE transceiver card 24 at theeast end of the link 30, serving the customer premises equipment (CPE)site 20. The U-BR1TE transceiver card 24 is, in turn, coupled over alocal loop (twisted tip/ring pair) 23 to a network termination interface(NT-1) circuit 21, to which customer premises equipment, such as an ISDNdata terminal, shown at 22, is coupled. In the non-extended systemconfiguration of FIG. 2, the local loop 13 from a respective line card12 in the central office switch 11, rather than being coupled to aU-BR1TE transceiver card, is coupled directly to the network terminationinterface (NT-1) circuit 21.

In either system configuration, since the network termination interface21 is customer-installed (and therefore locally powered at the customerpremises site 20, rather than being powered by the central office 10, asin the case of a conventional POTS telephone), the local telephoneservice provider is unable to interfere with the customer's choice ofequipment to be connected to the ISDN line, such as the installation ofequipment that provides a battery back-up in the event of a poweroutage.

Although the public service commissions of local jurisdictions wherecustomer premises equipment is installed require that telephone serviceproviders (regional Bell operating companies) ensure that each customerbe provided with emergency (911) telephone service, the service provideris currently not permitted to dictate that the customer install aparticular piece of equipment, such as one that will provide back-upbattery for the network termination interface during a power outage. Asa consequence, service providers customarily require their residentialcustomers to maintain a separate POTS line as an emergency adjunct tothe ISDN service, so that the residential customer is, in effect, forcedto subscribe to an additional form of ‘fire insurance’. Namely, theextra POTS line is intended to prevent residential customers from losingaccess to telephone service, particularly in the event of an emergency,where expedient 911 service may be critical. Such a requirementobviously constitutes a substantial cost penalty to the customer, who isfaced with both a potential installation fee, and an unwanted monthlybill for a normally unused POTS line.

SUMMARY OF THE INVENTION

In accordance with the present invention, the need to ensure continuoustelephone service to a residential customer premises served by an ISDNline, without requiring that the customer maintain an additional POTSline as an emergency back-up to the normally used ISDN service, issuccessfully addressed by a modification of conventional ISDN signallingcircuits and network termination interface components, together with anaugmentation of the communication control software employed therein, sothat, in the event of a loss of power to customer premises equipment, acommunication link between an auxiliary POTS telephone and an ISDNcommunication path to the central office may be established.

In accordance with a first embodiment of the invention, the U-BR1TE cardof an extended distance ISDN system, and network termination interfaceat the customer premises site are respectively replaced with a modifiedU-BR1TE card and a modified network termination interface, whichselectively provide auxiliary communication capability over the extendedISDN line with an auxiliary POTS telephone, that is connectable to themodified network termination interface. Advantageously, in this andother embodiments of the invention, there is no modification of thecentral office switch, per se, so that the integrity of the ISDNcommunication path with the central office line card remains unaffected.As a result, the central office equipment can continue to conductstandard ISDN communications with the customer premises equipment, eventhough the customer is employing a POTS back-up phone.

Pursuant to the first embodiment of the invention, the architecture ofthe U-BR1TE card is modified to include an auxiliary digital/analoginterface, an auxiliary loop relay, and a loss of power monitoringmechanism which is associated with the card's microcontroller. In theevent of an emergency POTS mode of operation, the microcontrolleroperates the loop relay and thereby substitutes the auxiliarydigital/analog interface in place of normally employed ISDN transceivercircuitry. Respective transmit and receive links of a PCM bus areterminated by way of a standard PCM bus interface unit which iscontrolled by the microcontroller and is also coupled to an ISDNU-transceiver interface. The ISDN U-transceiver interface customarilydirectly ports industry standard 2B1Q-formatted symbols with respectivetip and ring leads of a local twisted cable pair loop that services thecustomer premises equipment.

The auxiliary digital/analog interface contains a codec unit and asubscriber loop interface (SLI), which are controllably connected incircuit between the local loop and the PCM bus interface in dependenceupon the state of operation of the auxiliary loop relay. The SLI, whichperforms on-hook/off-hook detection, is coupled to each of a (10 KHz)tone detector and a dual tone multifrequency (DTMF) and pulse detector,outputs of which are coupled to the microcontroller. The tone detectoris employed as a wake-up tone detector and supplies an output signal tothe microcontroller, in response to the network termination interface atthe customer premises generating a 10 KHZ tone upon power-up. The DTMFdetector produces signals associated with tone signals (such as dialtones) sourced from the customer premises equipment.

The control software of microcontroller contains a loss of powermonitoring mechanism, which monitors the signalling condition on the tipand ring pair of the local loop by looking for a signalling conditionrepresentative of loss of power to the network termination interface.This loss of power condition may be detected, by examining data receivedat the U-transceiver interface for status information bits associatedwith the power status of the network termination interface, or may beidentified by a loss in synchronization of the data received by theU-transceiver interface from the local loop. To accommodate a very briefloss of power, such as a momentary interruption caused by a lightningstrike, without switching to the back-up mode, a filter mechanism isemployed, which requires that the power loss persist for a minimumduration. In response to detecting such a loss of power condition, themicrocontroller operates the auxiliary relay, thereby causing the localloop to be decoupled from the path for normal ISDN signal processing inthe U-transceiver interface and, instead, couples the local loop throughthe digital/analog interface to the PCM bus interface.

When placed in this auxiliary or emergency back-up POTS mode, controlsignals (either pulse or tone dialing signals) supplied over the localloop from the customer's POTS phone are output as standard (Q921/931)messages over the ISDN D channel from the microcontroller to the PCM businterface. The auxiliary digital/analog interface converts sampledanalog voice signals received over the local loop from the auxiliaryPOTS telephone into digital communication signals, such as 64 Kbpsdigitally formatted voice signals, that are coupled to the PCM businterface for transmission via a B channel portion of the ISDNcommunication link of an outgoing data stream to the central office.Conversely, in the receive direction, received digital signals from thePCM bus interface are coupled to the auxiliary digital/analog interface,which regenerates outgoing analog voice signals for application throughthe auxiliary relay to the local loop.

When power has been restored to the customer premises equipment, wherethe functionality of the circuitry within the network terminationinterface is designed to generate a 10 KHz tone on power-up, a signalfrom the 10 KHz tone detector causes the microcontroller to check for anON-HOOK condition on the loop, indicating that the POTS phone is not inuse. If the POTS phone is OFF-HOOK, the call is allowed to be completed.Upon verifying an ON-HOOK condition of the POTS phone, themicrocontroller deactivates the auxiliary relay, thereby decoupling thelocal loop from the auxiliary digital/analog interface, and recouplingthe local loop to the normal ISDN signal processing circuitry within thedigital communication signal U-transceiver interface.

Where the network termination interface is of the type that does nottransmit such a 10 KHz tone on power-up, the monitoring mechanism withinmicrocontroller may periodically deactivate the auxiliary relay when inan on-hook state, and thereby periodically decouple the auxiliarydigital/analog interface from the local loop, and then recouple thelocal loop to the ISDN U-transceiver interface. During each of theseperiodic change-overs, the transceiver attempts to reestablish digitalcommunication capability over the local loop with the networktermination interface. If it is unable to do so within a prescribedperiod of time, the microcontroller again switches the relay back to thePOTS mode configuration, and thereby returns the connection between thelocal loop and the auxiliary digital/analog interface, so as to decouplethe local loop from the ISDN transceiver.

The modified network termination interface includes an auxiliary POTSsignalling path and an associated loss of power-responsive relay. Inresponse to a loss of power, the auxiliary relay substitutes theauxiliary signalling path to a POTS phone in place of a normallyemployed ISDN signalling path to ISDN telephone equipment, so that thePOTS phone is connected to the modified U-BR1TE card.

In accordance with a second embodiment of the invention, the U-BR1TEcard of an extended distance system is replaced with a modified U-BR1TEcard and a smart jack is inserted between the modified U-BR1TE card andthe network termination interface. The smart jack is operative toconnect the local loop from the modified U-BR1TE card to the RJ45 jackof a conventional network termination interface provides separate RJ11and RJ45 connections to the auxiliary POTS phone and to the ISDNterminal equipment. An auxiliary relay in the smart jack operates in thesame manner as the auxiliary relay in the modified network terminationinterface architecture, switchably providing an ISDN connection channelfor tip/ring and power between a first RJ45 jack and a second RJ45 jackfor normal ISDN mode of operation, and an auxiliary path betweentip/ring leads of the first RJ45 jack to an RJ11 jack during POTS modeof operation.

Pursuant to a third embodiment of the invention for extended distanceISDN communications, the U-BR1TE card and the network terminationinterface at the customer premises site are respectively replaced with amodified U-BR1TE card and an integrated ISDN telephone and networktermination interface unit, which includes a POTS phone back-up. Theintegrated ISDN telephone and network termination interface unitcomprises a tip/ring interface ported to the local twisted cable pairloop from the modified U-BR1TE card, and a loss of power sensing relay.

In its normal powered condition, the relay is operative to provide apath through which a U-transceiver interface, codec and the SLI arecontrollably connected in circuit to the local loop and a hand setinterface. As a result, the customer is able to conduct standard ISDNvoice communications with the network in a conventional manner. The ISDNU-transceiver interface is controlled by a communications controlmicrocontroller.

In response to a loss of local power, the relay is de-energized, so thatpower is supplied through a POTS line hybrid interface, whereby internalloop power may be drawn from the local loop. This internal loop power iscoupled to the hand set interface, so as to support a back-up analogvoice channel to the POTS line hybrid interface from the hand set. As aconsequence the customer has a POTS analog link through the hybrid tothe local loop and the modified U-BR1TE card. When power is restored,the relay winding is again energized, so as to provide a circuit pathbetween the local loop and the ISDN U-transceiver interface.

In accordance with a fourth embodiment of the invention, the modifiednetwork termination interface of the extended distance system isreplaced by an integrated ISDN terminal adapter and network terminationinterface having a single jack/port, which is operative either as anISDN voice channel or as an emergency POTS back-up. This integrated ISDNterminal adapter and network termination interface is similar to themodified network termination interface, as it contains a normal ISDNsignalling path to which a POTS phone is coupled, and an associated lossof power-responsive relay switch, which by-passes the ISDN signallingpath and substitutes an auxiliary analog POTS phone back-up path inplace of the normally employed ISDN signalling path. As a consequence,the POTS phone may be connected directly via the local loop to themodified UBR1TE card associated with the customer premises site.

The integrated ISDN terminal adapter and network termination interfaceincludes a relay having a winding connected to the local power sourcesupplied by the customer, and a first pair of switch contacts connectedin circuit with the tip and ring leads of the local loop and first andsecond alternative tip and ring pairs. The first tip and ring pair iscoupled to provide a path for the normal 2B1Q ISDN signalling channelwith an ISDN transceiver unit. This ISDN transceiver unit is coupled toan attendant control processor, which is ported to local digital dataterminal equipment, which may be ISDN telephone or other ISDN terminalequipment. The other tip and ring pair is coupled to a second pair ofswitch contacts of the relay switch, which are ported via a tip and ringpair to the POTS jack/port. A further tip and ring pair is coupled viarelay switch contacts to an SLI/codec unit interfaced with theprocessor.

With local power being normally applied to the integrated ISDN terminaladapter and network termination interface, the relay winding isenergized, so that a first pair of switchable contacts of the relayswitch provide a circuit path between the tip and ring leads of thelocal loop to the U-transceiver interface. A second pair of switchablecontacts of the relay switch provide a circuit path between the tip andring leads of the POTS phone and the SLI/codec unit. In this normal modeof operation, the POTS phone is interfaced with the ISDN interfacecircuit functionality of the codec, SLI and transceiver components ofthe interface, so that it effectively appears to the modified U-BR1TEcard as a piece of ISDN data terminal equipment. Should there be a lossof local power, the ISDN signal processing circuitry within the modifiednetwork termination interface will become disabled, preventing the useof the POTS phone for normal ISDN communications. In this event, therelay winding is de-energized, causing the local loop 240 to beconnected directly to the POTS phone, by-passing the ISDN signalprocessing circuitry of the interface.

In addition to providing back-up emergency POTS service for extendeddistance ISDN applications, the present invention may also be employedto provide power outage back-up POTS service for a non-extended distanceISDN communication system, in which the local loop from a respectiveline card in the central office switch is coupled directly to thenetwork termination interface (NT1) circuit, rather than to a U-BR1TEtransceiver card for effecting extended distance communications via aPCM link.

Pursuant to a fifth embodiment of the present invention, loss of powerPOTS back-up service is provided to a non-extended distance ISDNcommunication system, wherein the network termination interface isreplaced by the modified network termination interface. As in theabove-described embodiments of the invention for extended distanceapplications, the integrity of the ISDN communication path between thenetwork termination interface and the central office switch remainsunaffected, so that the central office equipment continues to conductstandard ISDN communications with the customer premises equipment, eventhough the customer is again employing a POTS back-up phone.

In the fifth embodiment, since the modified network terminationinterface causes the analog signals of the POTS phone to be appliedthrough signal path directly to the local loop for transport to the linecard of the central office switch, it its necessary to replace the linecard with a modified line card, which is configured to replicate themodified U-BR1TE card configuration, described above.

In accordance with a sixth embodiment of the invention, for non-extendeddistance ISDN communications, the network termination interface at thecustomer premises site is replaced with a integrated ISDN telephone andnetwork termination interface unit which includes a POTS phone back-up,described above. In this embodiment, as in the fifth embodiment, sincethe integrated ISDN telephone and network termination interface unitalso causes the analog signals of the POTS phone to be applied to thelocal loop for transport to the line card of the central office switch,it its necessary to replace the line card with a modified line card,which is configured to replicate the modified U-BR1TE cardconfiguration, described above.

Pursuant to a seventh embodiment of the present invention, the modifiednetwork termination interface of the non-extended distance system isreplaced by the integrated ISDN terminal adapter and network terminationinterface. In addition, since the integrated ISDN terminal adapter andnetwork termination interface interfaces the POTS phone's analog signalswith the local loop to the line card of the central office switch, it isagain necessary to replace the line card with a modified line card thatis configured to replicate the modified U-BR1TE card, as describedabove.

In an eighth embodiment, for non-extended ISDN applications, similar tothe second embodiment for extended ISDN applications, rather than employthe modified network termination interface to provide the auxiliary POTSsignalling path and an associated loss of power-responsive relay switch,these auxiliary channel-connectivity functions are provided throughseparate smart jack module. This smart jack module connects the localloop from a modified line card in the central office switch to the RJ45jack of a conventional network termination interface and is operative toprovide separate RJ11 and RJ45 connections to the auxiliary POTS phoneand to the ISDN terminal equipment.

In accordance with a ninth embodiment of the present invention, a smartjack module is also used to connect the local loop to an RJ45 jack of aconventional network termination interface and is operative to provideseparate RJ11 and RJ45 connections to the auxiliary POTS phone and tothe ISDN terminal equipment. However, rather than replace the line cardin the central office switch with a modified line card, an ISDN POTSback-up interface is installed in the local loop.

The ISDN POTS back-up interface is configured similar to the modifiedU-BR1TE card. Respective tip and ring leads of the network side of thelocal loop are terminated by way of a network termination U transceiverinterface, which interfaces 2B1Q data with the network side of localloop. The network termination U transceiver interface is controlled by amicrocontroller and is also coupled via a first ISDN bus to a datarouter unit. The data router is coupled via a second ISDN bus to a looptermination U-transceiver interface, which interfaces 2B1Q data with thecustomer premises side of local loop. The data router eithertransparently and bidirectionally routes 2B+D data between the networkand loop transceivers, or routes 1B+D data between the networkU-transceiver and a codec within the auxiliary digital/analog interface,during POTS back-up mode. The microcontroller is coupled to the looptermination U-transceiver and to the data router. D channel data iscoupled between the microcontroller and the data router.

Like the modified U-BR1TE card, the auxiliary digital/analog interfaceof the ISDN POTS back-up interface also includes a codec and an SLI,which are controllably connected in circuit between a data bus to thedata router and tip and ring leads to first terminal contacts of therelay. The loop termination U-transceiver interface is coupled viarespective tip and ring leads to second terminal contacts of the relay.A pair of switchable relay arms are coupled to respective tip and ringleads of the customer premises side of the interface. The SLI is alsocoupled to each of a 10 KHz tone detector and a dual tone multifrequency(DTMF) and pulse detector respective outputs of which are coupled to themicrocontroller. The 10 KHz tone detector is employed as a wake-up tonedetector and supplies an output signal to the microcontroller inresponse to the network termination interface at the customer premisesgenerating a 10 KHz tone upon power-up. The DTMF detector producessignals associated with tone signals sourced from the customer premisesequipment.

As in the modified U-BR1TE card described previously, the controlsoftware employed by the microcontroller monitors the local loop leadsto the network termination interface, in order to determine the abilityof the network termination interface to provide normal telephone servicewith the customer's data terminal equipment (DTE). In response todetecting a loss of power condition, the microcontroller operates therelay, so that the tip and ring leads of the customer premises side ofthe local loop are decoupled from the tip and ring path for normal ISDNsignal processing to the loop termination U-transceiver unit and,instead, couples the local loop leads to the digital/analog interface.

When placed in this POTS back-up mode, control signals from thecustomer's POTS phone are translated into standard (Q921/931) messagesover D channel link to the data router for application to the D channeland transmission on the network side of the local loop by way of thenetwork termination U-transceiver interface. The digital/analoginterface converts sampled analog voice signals received from the POTStelephone into 64 Kbps digitally formatted voice signals, that arecoupled over ISDN bus to the data router for application via a B channelportion of the ISDN communication bus of the U-transceiver interface andtransmission therefrom as 2B1Q data over the network side of the localloop to the line card in the central office.

In the receive direction from the network side of the local loop,incoming 2B1Q signals from the line card are converted by the networkU-transceiver into 2B+D signals and applied via a ISDN bus to the datarouter. The data router couples the bearer (B) channel (coded voice)data from the network U-transceiver interface to the auxiliarydigital/analog interface, which regenerates outgoing analog voicesignals through the relay to the tip and ring leads of the customerpremises side of the local loop.

Similar to the operation of the modified U-BR1TE card described above,in response to power being restored to the customer premises equipment,where the network termination interface is designed to generate a 10 KHztone on power-up, a signal is coupled the 10 KHz tone detector to themicrocontroller, indicating that the POTS phone is not in use. If thePOTS phone is not in use, the microcontroller deactivates the relay,thereby decoupling the customer premises side of the local loop from theauxiliary digital/analog interface, and recoupling the loop to the looptermination U-transceiver interface.

As in the modified U-BR1TE card, where the network termination interfaceis of the type that does not transmit a 10 KHz tone on power-up, themicrocontroller may periodically deactivate the relay and therebyrepeatedly decouple the auxiliary digital/analog interface from thelocal loop, and then recouple the local loop to the loop terminationU-transceiver interface, which attempts to reestablish digitalcommunication capability over the local loop with the networktermination interface, as described above.

In accordance with a tenth embodiment of the invention, similar to theextended distance system architecture of the third embodiment, thenetwork termination interface at the customer premises site is replacedwith the integrated ISDN telephone and network termination interfaceunit, which includes a POTS phone back-up. As in the ninth embodiment,inorder to accommodate the analog signalling format of the POTS phone,rather than replace the line card in the central office switch with amodified line card, the ISDN POTS back-up interface is installed in thelocal loop.

Pursuant to an eleventh embodiment of the invention, the modifiednetwork termination interface of the non-extended distance system isreplaced by an integrated ISDN terminal adapter and network terminationinterface, described above. In addition, as in the ninth and tenthembodiments, in order to accommodate the analog signalling format of thePOTS phone, rather than replace the line card in the central officeswitch with a modified line card, the ISDN POTS back-up interface isinstalled in the local loop between the line card and the integratedISDN terminal adapter and network termination interface.

Pursuant to a twelfth embodiment of the present invention, the networktermination interface of the non-extended distance system is replaced bythe modified network termination interface. Also, as in the ninththrough eleventh embodiments, in order to maintain integrity of the ISDNcommunication path between the network termination interface and thecentral office switch, rather than replace the line card in the centraloffice switch with a modified line card, the ISDN POTS back-up interfaceis installed in the local loop between the line card and the integratedISDN terminal adapter and network termination interface.

Pursuant to a thirteenth embodiment of the invention, the eleventhembodimentis modified so that the integrated ISDN terminal adapter andnetwork termination interface is replaced by a modified configuration toprovide for connection to an ISDN S/T interface port. Rather than havinga connection for customer interface data to data terminal equipment, thecontrol processor is coupled to an S/T interface which interfaces a 2B+Dchannel with a U-interface and is coupled to via an S/T port to an ISDNterminal equipment, terminal adapter. The D channel is coupled betweenthe processor and the U-interface, while the B channel is coupledbetween the U-interface and the SLI and codec.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates a reduced complexity example of atypical extended distance integrated services digital network (ISDN)communication system;

FIG. 2 diagrammatically illustrates a non-extended distance ISDNcommunication system;

FIG. 3 diagrammatically illustrates the manner in which a U-BR1TE cardof the extended distance ISDN communication system of FIG. 1 may beupgraded in accordance with a first embodiment of the invention, toselectively substitute an auxiliary digital/analog interface in place ofthe normally employed ISDN signalling circuitry, for emergency (loss ofpower) POTS mode of operation;

FIG. 4 diagrammatically illustrates the architecture of a modifiedU-BR1TE card which interfaces the customer premises end of a PCM linkwith a modified network termination interface;

FIG. 5 diagrammatically illustrates the architecture of a modifiednetwork termination interface;

FIG. 6 diagrammatically shows a second embodiment of the invention,wherein a ‘smart’ jack module connects the local loop from a modifiedU-BR1TE card to an RJ45 jack of a conventional network terminationinterface;

FIG. 7 diagrammatically illustrates the architecture of a smart jack;

FIG. 8 diagrammatically illustrates a third embodiment of the inventionfor extended distance ISDN communications, wherein a U-BR1TE card and anetwork termination interface at the customer premises site arerespectively replaced with a modified U-BR1TE card, and an integratedISDN telephone and network termination interface unit, which includes aPOTS phone back-up;

FIG. 9 is a detailed illustration of an integrated ISDN telephone andnetwork termination interface unit;

FIG. 10 diagrammatically illustrates a fourth embodiment of the presentinvention, wherein the modified network termination interface of theextended distance system of FIG. 3 is replaced by an integrated ISDNterminal adapter and network termination interface;

FIG. 11 is a detailed illustration of an integrated ISDN terminaladapter and network termination interface;

FIG. 12 shows a fifth embodiment of the invention, wherein loss of powerPOTS back-up service is provided to a non-extended distance ISDNcommunication system, with the network termination interface beingreplaced by the modified network termination interface of FIG. 5;

FIG. 13 diagrammatically illustrates a sixth embodiment of theinvention, for non-extended distance ISDN communications, wherein thenetwork termination interface at the customer premises site is replacedwith the integrated ISDN telephone and network termination interfaceunit;

FIG. 14 diagrammatically illustrates a seventh embodiment of the presentinvention, wherein the modified network termination interface of thenon-extended distance system of FIG. 2 is replaced by an integrated ISDNterminal adapter and network termination interface;

FIG. 15 diagrammatically illustrates an eighth embodiment of theinvention for non-extended ISDN applications, wherein auxiliarychannel-connectivity functions are provided through a smart jack modulewhich connects the local loop from a modified line card in a centraloffice switch to an RJ45 jack of a network termination interface;

FIG. 16 diagrammatically illustrates a ninth embodiment of the presentinvention, wherein a smart jack module connects the local loop to anRJ45 jack of a network termination interface and is operative to provideseparate RJ11 and RJ45 connections to an auxiliary POTS phone and toISDN terminal equipment;

FIG. 17 illustrates the details of an ISDN POTS back-up interface;

FIG. 18 diagrammatically illustrates a tenth embodiment of the presentinvention, wherein the network termination interface at the customerpremises site is replaced with an integrated ISDN telephone and networktermination interface unit, and which includes an integrated ISDNtelephone and network termination interface of FIG. 11;

FIG. 19 diagrammatically illustrates an eleventh embodiment of theinvention, wherein the modified network termination interface of thenon-extended distance system of FIG. 2 is replaced by the integratedISDN terminal adapter and network termination interface of FIG. 11 andwhich includes an integrated ISDN telephone and network terminationinterface of FIG. 11;

FIG. 20 diagrammatically illustrates a twelfth embodiment of the presentinvention, wherein the network termination interface of the non-extendeddistance system of FIG. 2 is replaced by the modified networktermination interface of FIG. 5, and includes an integrated ISDNtelephone and network termination interface of FIG. 11;

FIG. 21 diagrammatically illustrates a thirteenth embodiment of theinvention, wherein the eleventh embodiment is modified so that theintegrated ISDN terminal adapter and network termination interface isreplaced by a modified configuration to provide for connection to anISDN SIT interface port; and

FIG. 22 is a detailed illustration of the modified integrated ISDNterminal adapter and network termination interface employed in theembodiment of FIG. 21.

DETAILED DESCRIPTION

Before describing in detail the new and improved mechanism for providingauxiliary, substitute POTS capability at an ISDN customer premises, itshould be observed that the present invention resides primarily in themodification of conventional ISDN signalling circuits and networktermination interface components, together with an augmentation of thecommunication control software employed therein, that enables ISDNsignalling capability monitoring mechanisms in each of the centraloffice and customer premises equipments sites to selectively decouplethe local loop from the normal ISDN signal processing circuitry in thedigital communication signal transceiver and the ISDN customer premisesequipment and, in their place, switch the local loop to an auxiliarydigital/analog interface and a back-up POTS telephone, so as to installan operative communication link between the POTS telephone and the ISDNcommunication path to the central office. The details of the circuitryof the ISDN transceiver and network termination interface units areotherwise essentially unaffected.

Accordingly, the structure, control and arrangement of theseconventional circuits and components have been illustrated in thedrawings by readily understandable block diagrams which show only thosespecific details that are pertinent to the present invention, so as notto obscure the disclosure with structural details which will be readilyapparent to those skilled in the art having the benefit of thedescription herein. Thus, the block diagram illustrations of the Figuresdo not necessarily represent the mechanical structural arrangement ofthe exemplary system, but are primarily intended to illustrate the majorstructural components of the system in a convenient functional grouping,whereby the present invention may be more readily understood.

As pointed out previously, because the network termination interface 21(whether it be installed in the extended distance system of FIG. 1 orthe non-extended distance system of FIG. 2) is a customer-installedpiece of equipment, it is locally powered, and may not have a batteryback-up, so that there is no assurance that the customer will havetelephone service capability in the event of a power outage at thecustomer premises site. Since the telephone service provider is notallowed to compel the customer to install equipment that possessesback-up battery, then, in order to ensure emergency telephonecommunication capability, the service provider customarily requires thata residential customer maintain a separate POTS line as an adjunct tothe ISDN line.

Pots Back-up for Extended Distance ISDN Communications Embodiment 1Modifed U-BR1TE Card, Modified NT-1 Interface FIGS. 3, 4 and 5

Pursuant to a first embodiment of the invention, diagrammaticallyillustrated in FIG. 3, for extended distance ISDN communications, thisproblem is successfully obviated by replacing the U-BR1TE card 24 andnetwork termination interface 21 at the customer premises site with amodified U-BR1TE card 24M (shown in detail in FIG. 4, to be described)and a modified network termination interface (NT-1) 21M (shown in detailin FIG. 4, to be described). As will be described, these upgraded units24M and 24M selectively provide auxiliary communication capability overthe extended ISDN line with an auxiliary POTS telephone 25 that isconnectable by the customer to the modified network terminationinterface 21M. In accordance with this first embodiment of theinvention, the integrity of the ISDN communication path with the centraloffice line card remains unaffected, there being no modification ofcentral office equipment, so that the central office equipment continuesto conduct standard ISDN communications with the customer premisesequipment, even though the customer is employing a POTS back-up phone.

More particularly, FIG. 4 diagrammatically illustrates the architectureof a modified U-BR1TE card 24M, which interfaces the customer premisesend of the PCM link 30 with a modified NT-1 21M, as including anauxiliary digital/analog interface 250, a loop relay 260 and, associatedwith the card's microcontroller 220, a loss of power monitoringmechanism, which, in the event of an emergency POTS mode of operation,is operative to selectively control the operation of the loop relay 260,and thereby control the substitution of the auxiliary digital/analoginterface 250 in place of the normally employed ISDN transceivercircuitry.

For this purpose, in the modified U-BR1TE card architecture of FIG. 4,respective transmit and receive links 201 and 203 of the T1 PCM bus 30are terminated by way of a standard PCM bus interface unit 210. PCM businterface 210 is controlled by an attendant microcontroller 220 via acontrol link 215, and is also coupled via an ISDN bus 225 to an ISDNtransceiver unit 230. Microcontroller 220 is coupled to ISDN transceiverunit 230 via a control link 235. ISDN bus 225 conveys a standard pair of(64 kb/s) bearer (B) channels and a single (16 kb/s) data (D) channel as(2B+D) data traffic. ISDN transceiver unit 230 customarily directlyports industry standard 2B1Q-formatted symbols with respective tip andring leads 241 and 242 of a local twisted cable pair loop 240, thatservices the customer premises equipment.

The modified U-BR1TE card architecture of FIG. 4 further includes anauxiliary digital/analog interface 250, which contains a codec unit 251and a subscriber loop interface (SLI) 253. The codec and the SLI arecontrollably connected in circuit between the local loop 240 and the PCMbus interface 210, based upon the state of operation of an auxiliaryloop relay 260. The auxiliary loop relay 260 is connected in circuitwith the tip and ring leads 241 and 242 of the local loop 240 to thenetwork interface, and first and second alternative tip and ring pairs245 and 246.

Tip and ring pair 245 is coupled to provide the standard 2B1Q ISDNsignalling channel with the transceiver unit 230, while tip and ringpair 246 is coupled to provide an auxiliary POTS signalling channel froma customer's back-up analog POTS phone 25 with auxiliary digital/analoginterface 250. The switch contacts 261, 263 of relay 260 are normallycoupled to provide a circuit path between the tip and ring leads of thelocal loop and the tip and ring pair 245 of transceiver unit 230. In theevent of a loss of power at the network termination, relay 260 isoperated by a relay driver 226, which is coupled over link 227 frommicrocontroller 220, so as to switch the local loop 240 in circuit withtip and ring pair 246, as will be described.

The subscriber loop interface (SLI) 253 is also coupled to each of a 10KHz tone detector 268 and a dual tone multifrequency (DTMF) and pulsedetector 270, outputs 262 and 272 of which are coupled tomicrocontroller 210. 10 KHz tone detector 268 is employed as a wake-uptone detector and supplies an output signal over line 262 to themicrocontroller 210, in response to the network termination interface atthe customer premises generating a 10 KHZ tone upon power-up. DTMFdetector 270 produces signals on line 272 associated with tone signals(such as dial tones) sourced from the customer premises equipment 22.

As noted previously, the control software employed by microcontroller220 is modified in accordance with the invention to continuously monitorthe local loop 240 to the network termination interface 21, in order todetermine the ability of the network termination interface to providenormal telephone service with the customer's data terminal equipment(DTE) 22. In particular, the control software of microcontroller 220contains a loss of power monitoring mechanism, which monitors thesignalling condition on the tip and ring pair 245 via transceiver unit230, by looking for a signalling condition representative of loss ofpower to the network termination interface. This loss of power conditionmay be detected, for example, by examining data received at thetransceiver 230 from the local loop 240 for status information bitsassociated with the power status of the network termination interface.The loss of power condition may also be identified by a loss insynchronization of the data received by transceiver 230 from the localloop 240.

Regardless of the mechanism employed, in response to detecting a loss ofpower condition, the microcontroller 220 generates a switch controloutput signal on line 227 to relay driver 226, so as to operate relay260 and thereby cause the tip and ring leads 241 and 242 of the localloop 240 to be decoupled from the tip and ring path 245 for normal ISDNsignal processing in transceiver unit 230 and, instead, couple the localloop 240 through the auxiliary tip and ring pair 246 to digital/analoginterface 250 to the PCM bus interface 210.

When placed in this ‘auxiliary POTS’ mode, control signals (pulse ortone dialing signals) from the customer's POTS phone via the local loop240 are output as standard (Q921/931) messages over D channel link 214from microcontroller 220 to the PCM bus interface 210. The auxiliarydigital/analog interface 250 is operative to convert sampled analogvoice signals received over the local loop 240 from the auxiliary analog(POTS) telephone 25 into digital communication signals, such as 64 Kbpsdigitally formatted voice signals, that are coupled over link 255 to thePCM bus interface 210 for transmission via a B channel portion of theISDN communication link of an outgoing T1 data stream over transmit bus201. In the receive direction from receive bus 203, received T1 signalsare coupled over link 255 from the PCM bus interface 210 to theauxiliary digital/analog interface 250, which regenerates outgoinganalog voice signals for application over tip/ring pair 246 throughrelay 260 to the local loop 240.

When power has been restored to the customer premises equipment(corresponding to a signalling recovery condition), if the functionalityof the circuitry within the network termination interface is designed togenerate a 10 KHZ tone on power-up, a signal is coupled over line 262from 10 KHz tone detector 268 to microcontroller 220, indicating thatthe POTS phone 25 is not in use (OFF-HOOK). (If the POTS phone 25 iscurrently OFF-HOOK, the call is allowed to be completed.)Microcontroller 220 then deactivates relay 260, thereby decoupling thelocal loop 250 from the auxiliary digital/analog interface 250, andrecoupling the local loop 250 to the normal ISDN signal processingcircuitry within the digital communication signal transceiver unit 230.

Where the network termination interface is of the type that does nottransmit such a 10 KHz tone on power-up, the monitoring mechanism withinmicrocontroller 220 may periodically deactivate relay 260 and therebyperiodically decouple the auxiliary digital/analog interface 250 fromthe local loop 240, and then recouple the local loop to the ISDNtransceiver 230. During each of these periodic change-overs, transceiver230 attempts to reestablish digital communication capability over thelocal loop 240 with the network termination interface 21. If it isunable to do so within a prescribed period of time (e.g. five seconds),the microcontroller 220 again switches the relay 260 back to the POTSmode configuration, and thereby returns the connection between the localloop 240 and the auxiliary digital/analog interface 250, so as todecouple the local loop from the ISDN transceiver 230.

FIG. 5 diagrammatically illustrates the architecture of a modifiednetwork termination interface 21M as including an auxiliary POTSsignalling path 290 and an associated loss of power-responsive relayswitch 310. As will be described, upon loss of power, the auxiliaryrelay switch 310 substitutes the auxiliary signalling path 290 to a POTSphone 25, in place of a normally employed ISDN signalling path to ISDNtelephone equipment 325, so that the POTS phone 25 is connected to themodified U-BR1TE card 24M of FIG. 4, described above.

More particularly, the modified network termination interface 21M ofFIG. 5 includes a relay switch 310, having a winding 311 connected to arelay (winding) driver 317, which is controlled by an attendant controlprocessor 318. Relay switch contacts 312 are connected in circuit withthe tip and ring leads 241 and 242 of the local loop 240, and first andsecond alternative tip and ring pairs 315 and 316. A loop currentdetector (such as an optoisolator circuit) 319 is coupled in one of thetip and ring links of tip/ring pair 316, and has its output coupled tocontrol processor 318.

Tip and ring pair 315 is coupled to provide a path for the normal 2B1QISDN signalling channel with an ISDN transceiver unit, shown in brokenlines 320. The ISDN transceiver unit 320 comprises an ISDN transceiver321 and an associated S/T transceiver 323, which is ported to an RJ45jack 324, for connection to ISDN-based customer equipment, such as anISDN telephone 325 or other ISDN terminal equipment. The other tip andring pair 316 is coupled to an auxiliary POTS termination jack 330 (e.g.a standard RJ11 jack), to which a customer may connect a standard analogtelephone set 25.

Similar to the relay 260 of the modified U-BR1TE card 24M of FIG. 4, theswitchable contacts of relay switch 310 are normally coupled to providea circuit path between the tip and ring leads 241 and 242 of local loop240 and the tip and ring pair 315 to transceiver unit 320. In the eventof a loss of power, a drive signal to relay winding driver 317 will nolonger be supplied by control processor 318. As a consequence, relaywinding 311 becomes de-energized, causing the relay switch contacts 312to translate to the (auxiliary POTS back-up) position shown in FIG. 5.In this position, a back-up circuit path is provided between the tip andring leads 241 and 242 of local loop 240 and the tip and ring pair 316to the auxiliary POTS termination jack 330, thereby allowing acustomer-installed standard analog telephone set 25 to be used in placeof the ISDN telephone equipment 325.

As described previously with reference to the modified U-BR1TE card 24Mof FIG. 4, when the customer uses the auxiliary POTS phone 25 to placean outgoing call, pulse or tone dialing signals generated by the handset25 are coupled (over the alternative path through relay 310 of themodified network termination interface) via the local loop 240 to DTMFand pulse detector 270, causing microcontroller 220 to output signalsover the D channel link 214 to the PCM bus interface. Once the call isconnected, the auxiliary digital/analog interface 250 is operative toconvert sampled analog voice signals received over the local loop 240from the auxiliary analog telephone 25 into digital communicationsignals (64 Kbps digitally formatted voice signals), that are coupledover link 255 to the PCM bus interface 210 for transmission in a Bchannel of the ISDN communication link of an outgoing T1 data streamover transmit bus 201. Conversely, in the receive direction, thedigital/analog interface 250 is operative to convert standard digital(e.g. Q921/931) messages from the network in order to ring the auxiliaryPOTS phone 25, and applies regenerated analog voice signals over localloop 240 and relay 310 to path 316 for application to the auxiliary POTSphone 25.

When power is restored to the network termination equipment,microcontroller 318, upon re-initialization, controllably supplies arelay winding drive signal to relay driver 317. To allow for thecompletion of a call via the POTS phone 25, processor 318 monitors theoutput of loop current detector 319, to determine whether or not a POTSphone call is in progress (indicated by the presence of loop currentthrough the tip/ring pair 316). If such a POTS phone call is in progresswhen power is restored, microcontroller 318 does not immediately apply arelay energizing signal to driver 317, but waits until the output ofloop current detector 319 has changed state, indicating that loopcurrent is no longer flowing through tip/ring pair 316. Processor 318thereupon reasserts a drive input signal to relay driver 317, therebycausing the relay switch contacts 312 to return to their normal states,described above, so as to provide a circuit path between the tip andring leads 241 and 242 of local loop 240 and the tip and ring pair 315,and thereby a path for the normal ISDN signalling channel with ISDNtransceiver unit 320. Where the transceiver 320 generates a 10 KHz toneon power-up, the tone signal is transmitted over the local loop 240 anddetected by 10 KHZ tone detector 268. Microcontroller 220 thendeactivates relay 260, thereby decoupling the local loop 240 from theauxiliary digital/analog interface 250, and recoupling the local loop tosignal transceiver unit 230.

Embodiment 2—Modified U-BR1TE Card with Smart Jack Connection to NT-1Interface FIGS. 6 and 7

Rather than install a modified network termination interface 21M of FIG.5 to provide the auxiliary POTS signalling path and an associated lossof power-responsive relay switch, these auxiliary channel-connectivityfunctions may be effected through a separate ‘smart’ jack module, suchas that illustrated at 26 in a second embodiment of the inventiondiagrammatically shown in FIG. 6, which connects the local loop 240 fromthe modified U-BR1TE card to the RJ45 jack of a conventional networktermination interface 21 and is operative to provide separate RJ11 andRJ45 connections to the auxiliary POTS phone 25 and to the ISDN terminalequipment 22, respectively.

The architecture of ‘smart’ jack 26 is diagrammatically shown in FIG. 7as having has a first RJ45 jack 410, which connects directly to the RJ45jack of a standard network termination interface, corresponding to theRJ45 jack of a conventional network termination interface 21. A firstlead 411 of the set of local power leads 413 of the RJ45 jack 410 iscoupled directly to a second RJ45 jack 420, to which the local loop 240is ported. A second lead 412 of the local power leads 413 of the RJ45jack is coupled directly through a winding 425 of a relay 430 to secondRJ45 jack 420. Respective tip and leads 414, 415 of RJ45 jack 410 arecoupled to first contacts 431 of a set of fixed relay contacts 435.Respective tip and ring leads 441, 442 of an RJ11 jack 440 for auxiliaryPOTS phone 25 are coupled to second contacts 432 of the set of fixedrelay contacts 430. Moveable contacts 433 of relay 430 are coupled totip/ring leads 412, 422 of the second RJ45 jack 420.

Relay 430 in the ‘smart’ jack of FIG. 7 operates in the same manner asrelay 310 in the modified network termination interface architecture ofFIG. 5, described above, providing an ISDN connection channel fortip/ring and power between the first RJ45 jack 410 and second RJ45 jack420, for normal ISDN mode of operation, and an auxiliary path betweenthe tip/ring leads of the first RJ45 jack to the RJ11 jack 440, duringPOTS mode of operation. As in the modified network termination interface21M of FIG. 5, power from the local power source 300 may be coupledthrough an intermediate switch (not shown), which may be manuallyoperated by the customer, so as to prevent a POTS phone call from beinginterrupted when power is restored.

Embodiment 3—Modified U-BR1TE Card with Integrated ISDN Phone havingPots Back-up FIGS. 8 and 9

FIG. 8 diagrammatically illustrates a third embodiment of the inventionfor extended distance ISDN communications, wherein the U-BR1TE card 24and network termination interface 21 at the customer premises site arerespectively replaced with the modified U-BR1TE card 24M of FIG. 4,described above, and an integrated ISDN telephone and networktermination interface unit 22M, which includes a POTS phone back-up.

The integrated ISDN telephone and network termination interface unit 22Mis shown in detail in FIG. 9 as comprising a tip/ring interface 500which has respective links 501 and 503 ported to the respective tip andring leads 241 and 242 of the local twisted cable pair loop 240 from themodified U-BR1TE card 24M of FIG. 4. Tip link 501 is coupled to a firstswitchable arm 511 of a relay 510, while ring link 503 is coupled to asecond switchable arm 513 of a relay 510. Relay 510 includes a winding520, which is normally energized by a relay driver 527, under thecontrol of a communications control processor 550.

In response to a loss of power, a drive signal is no longer applied torelay driver 527 by control processor 550, thereby de-energizing relaywinding 520 and causing its switchable arms 511 and 512 to translate totheir ‘loss of power’ positions shown in FIG. 9, wherein switchable arms511 and 513 are respectively connected through a first pair of lines 521and 523 to the tip and ring ports of a POTS line hybrid interface 530,which provides local loop power to a pair of lines 531 and 532 and aninternal bidirectional communication line 533. In their normalISDN-connective positions, with relay winding 520 energized, switchablearms 511 and 513 are respectively connected through a second pair oflines 525 and 526 to the tip and ring ports of an ISDN transceiver (Uinterface) unit 540, corresponding to that of ISDN transceiver 230 ofFIG. 4).

In the normally locally powered condition of the customer premisesequipment, ISDN transceiver unit 540 ports 2B1Q-formatted symbols onetip and ring pair 525 and 526 through relay 510 to port 500.

ISDN Transceiver 540 is controlled by control microcontroller 550 via acontrol link 545. ISDN transceiver 540 is also coupled via link 555 to acodec 560, which is interfaced via link 533 with POTS line hybridinterface 530 and a hand set interface unit 570. Hand set interface 570has an associated hook switch 575 and hand set 580 through which thecustomer conducts ISDN voice communications with the network.Microcontroller 550 has an auxiliary data port 552 (e.g. an RS-232 port)for external digital data communications.

During normal ISDN operation, with local power applied (relay winding520 energized by relay driver 527 under the control of control processor550), the switchable arms 511 and 513 of relay 510 are in the positionsopposite those shown in FIG. 9, so that U interface 540 and codec 560and the SLI are controllably connected in circuit through the contactsof powered relay 510 between port 500 to the local loop and the hand setinterface 570. As a result, the customer is able to conduct standard2B1Q-formatted ISDN voice communications with the network in aconventional manner.

In the event of a loss of local power, however, a relay drive signal isno longer output by microcontroller 550 to relay driver 527, so thatrelay winding 520 is de-energized, and the switchable arms 511 and 513are respectively connected through lines 521 and 523 to the tip and ringports of a POTS line hybrid interface 530, whereby internal loop powermay be drawn via port 500 from the local loop 240. This internal looppower is coupled via links 531 and 533 to the hand set interface 570, soas to support a back-up analog voice channel via link 533 to the POTSline hybrid interface 530 from the hand set 580. In this manner thecustomer has a POTS analog link through the hybrid to the local loop 240and thereby to the modified U-BR1TE card 24M of FIG. 4, described above.

When power is restored to the customer premises equipment,microcontroller 550, upon re-initialization, controllably supplies arelay winding drive signal to relay driver 527. To allow for thecompletion of a call via the hybrid 530, processor 550 monitors thestate of hook switch 575, to determine whether or not a POTS phone callis in progress (indicated by the handset 580 being off-hook). If such aPOTS phone call is in progress when power is restored, microcontroller550 does not immediately apply a relay energizing signal to driver 527,but waits until the output of the hook switch 575 has changed state,indicating that the customer has replaced the hand set 580 back in itscradle, terminating the POTS phone call. Processor 550 thereuponreasserts a drive input signal to relay driver 527, thereby causing therelay switch contacts 511 and 513 to return to their normal states,described above, so as to provide a circuit path between the tip andring leads 501 and 502 of the loop 500 and tip and ring leads 525 and526 to the ISDN interface 540. Where transceiver 540 generates a 10 KHztone on power-up, the tone signal is transmitted over the local loop 240and detected by the 10 KHZ tone detector 268 in the modified BR1TE card24M, as described previously.

Embodiment 4—Modified U-BR1TE Card with Integrated ISDN TerminalAdapter, NT-1 with Pots Port FIGS. 10 and 11

In accordance with a fourth embodiment of the present invention,diagrammatically illustrated in FIG. 10, the modified networktermination interface NT-1 21 of the extended distance system of FIG. 3is replaced by an integrated ISDN terminal adapter and networktermination interface 21M2, shown in detail in FIG. 11, described below.The integrated ISDN terminal adapter and network termination interface21M2 is similar to the modified network termination interfacearchitecture of FIG. 5 in that it includes a normal ISDN signalling path(to which a POTS phone is coupled) and an associated loss ofpower-responsive relay switch, which by-passes the ISDN signalling pathand substitutes an auxiliary analog POTS phone path in place of thenormally employed ISDN signalling path, so that the POTS phone may beconnected directly via the local loop 240 to the modified U-BR1TE card24M associated with the customer premises site.

More particularly, the integrated ISDN terminal adapter and networktermination interface 21M2 of FIG. 11 includes a relay switch 610,having a first winding 608 connected to a relay driver 609. Relay driver609 receives a drive signal from a supervisory control microprocessor630, which is ported via a digital data interface port 635 to localdigital data terminal equipment, which may be ISDN telephone or otherISDN terminal equipment. A first pair of switch contacts 612 and 613 ofrelay switch 610 are connected in circuit with the tip and ring leads23T and 23R of the local loop 23 and first and second alternative tipand ring pairs 615 and 616.

The first tip and ring pair 615 is coupled to provide a path for thenormal 2B1Q ISDN signalling channel with an ISDN transceiver unit 620,which is coupled to control processor 630. The other tip and ring pair616 is coupled to a second pair of switch contacts 614 and 615 of asecond relay switch 627, which has a relay winding 628 connected to arelay driver 629. Like relay driver 609, relay driver 629 receives adrive signal from supervisory control microprocessor 630. Switchcontacts of relay 627 are ported via a tip and ring pair 25T and 25R toPOTS phone 25. A further tip and ring pair 621 and 622 are coupled fromswitch contacts 618 and 619, respectively, to an SLI/codec unit 640,which is interfaced with processor 630.

When local power is normally applied, processor 630 supplies driverenergizing signals to each of relay drivers 609 and 629, so as toenergize each of relay windings 608 and 628. As a result, switchablecontacts 612 and 613 of relay switch 610 provide a circuit path betweenthe tip and ring leads 241 and 242 of the local loop 240 via the tip andring pair 615 to transceiver unit 620. Also, switchable contacts 614 and615 of relay switch 627 provide a circuit path between the tip and ringleads 25T and 25R of the POTS phone 25 and switch contacts 618 and 619,respectively, so that the POTS phone is connected to the SLI/codec unit640. In this normal mode of operation, the POTS phone 25 is interfacedwith the ISDN interface circuit functionality of the codec, SLI andtransceiver components of the interface, so that it effectively appearsto the modified U-BR1TE card 24M as a piece of ISDN data terminalequipment.

Should there be a loss of local power, however, the ISDN signalprocessing circuitry within the modified network termination interface21M2 of FIG. 11 will become disabled, preventing the use of the POTSphone for normal ISDN communications. In this event, control processor630 no longer supplies relay driver energizing signals to relay drivers609 and 629, so that each of relay windings 608 and 628 is de-energized,causing switch contacts 612, 613, 614 and 615 to transition to thepositions shown in FIG. 11, whereby the tip and ring leads 241 and 242of the local loop 240 are directly connected to the tip and ring leads25T and 25R, respectively of the POTS phone 15, by-passing the ISDNsignal processing circuitry of the interface.

A loop current detector 624 is coupled in circuit with the tip/ring pathbetween the local loop 23 and the POTS phone 25. When power is restored,microcontroller 630, upon re-initialization, controllably supplies arelay winding drive signal to each of relay drivers 609 and 629. Toallow for the completion of a call via switched tip/ring path, processor630 monitors the state of loop current detector 624, to determinewhether or not a POTS phone call is in progress (indicated by thepresence of loop current). If such a POTS phone call is in progress whenpower is restored, microcontroller 630 does not immediately apply arelay energizing signal to drivers 609 and 629, but waits until theoutput of the loop current detector 624 has changed state, indicatingthat the customer has gone on-hook, terminating the call. Processor 630thereupon reasserts drive input signals to relay drivers 609 and 629,thereby causing the relay switch contacts to return to their normalstates, described above.

Pots Back-up for Non-extended Distance ISDN Communications

As pointed out above, in addition to providing back-up emergency POTSservice for extended distance ISDN applications, the present inventionmay also be employed to provide emergency (loss of power) back-up POTSservice for a non-extended distance ISDN communication system, in whichthe local loop from a respective line card in the central office switchis coupled directly to the network termination interface (NT-1) circuit,rather than to a UBR1TE transceiver card for effecting extended distancecommunications via the (distance-extending) PCM (fiber optic) link.

Embodiment 5—Modified Line Card, Modified NT-1 Interface FIG. 12

Pursuant to a fifth embodiment of the present invention, loss of powerPOTS back-up service is provided to the non-extended distance ISDNcommunication system diagrammatically illustrated in FIG. 12, whereinthe network termination interface NT-1 21 of the non-extended distancesystem of FIG. 2 is replaced by the modified network terminationinterface NT-1 24M, shown in detail in FIG. 5, described above. As inthe previous embodiments of the invention for extended distanceapplications, the integrity of the ISDN communication path (local loop)between the network termination interface and the central office switchremains unaffected, so that the central office equipment continues toconduct standard ISDN communications with the customer premisesequipment, even though the customer is again employing a POTS back-upphone.

In this embodiment, since the modified network termination interfaceNT-1 24M causes the analog signals of the POTS phone 25 to be appliedthrough signal path 290 directly to the local loop 13 for transport tothe line card of the central office switch, it its necessary to replacethe line card with a modified line card 12M, which is configured toreplicate the modified U-BR1TE card 24M configuration of FIG. 4. When soinstalled, the control software employed by microcontroller 220 withinthe modified U-BR1TE replacement configured line card 12M continuouslymonitors the local loop (here, loop 13) in order to determine theability of the modified network termination interface NT-1 24M toprovide normal telephone service with the customer's data terminalequipment (DTE) 22. In response to detecting a loss of power condition,the microcontroller 220 within the modified line card 12M generates aswitch control output signal that operates the relay 260 and therebycauses the tip and ring leads of the local loop 13 to be decoupled fromthe tip and ring path for normal ISDN signal processing in transceiverunit 230 and, instead, couples the local loop 240 through the auxiliarytip and ring pair to the digital/analog interface 250 to the local loop.

When placed in the POTS mode, control signals from the customer's POTSphone applied to the local loop 13 are output as standard (Q921/931)messages over the D channel link from the microcontroller 220. Asexplained above, the auxiliary digital/analog interface 250 is operativeto convert sampled analog voice signals received over the local loopfrom the auxiliary analog (POTS) telephone 25 into (64 Kbps) digitallyformatted voice signals, for transmission via a B channel portion of theISDN communication link. In the receive direction, the auxiliarydigital/analog interface 250 regenerates outgoing analog voice signalsfor application via the relay to the local loop 13.

Embodiment 6—Modified Line Card with Integrated ISDN Phone having PotsBack-up FIG. 13

FIG. 13 diagrammatically illustrates a sixth embodiment of theinvention, for non-extended distance ISDN communications, wherein thenetwork termination interface 21 at the customer premises site isreplaced with the integrated ISDN telephone and network terminationinterface unit 22M, which includes a POTS phone back-up, shown in FIG.9, described above. In this embodiment, as in the fifth embodiment ofFIG. 12, since the integrated ISDN telephone and network terminationinterface unit 22M, which includes a POTS phone back-up, also causes theanalog signals of the POTS phone 25 to be applied to the local loop 13for transport to the line card of the central office switch, it itsnecessary to replace the line card with a modified line card 12M, whichis configured to replicate the modified U-BR1TE card 24M configurationof FIG. 4, as described above.

Embodiment 7—Modified Line Card with Integrated ISDN Terminal Adapter,NT-1 with Pots Port FIG. 14

Pursuant to a seventh embodiment of the present invention,diagrammatically illustrated in FIG. 14, the modified networktermination interface NT-1 21 of the non-extended distance system ofFIG. 2 is replaced by the integrated ISDN terminal adapter and networktermination interface 21M2, shown in detail in FIG. 11, described above.In addition, since the integrated ISDN terminal adapter and networktermination interface 21M2, shown in detail in FIG. 11, interfaces thePOTS phone 25 analog signals with the local loop 13 to the line card ofthe central office switch, it is again necessary to replace the linecard with a modified line card 12M, configured to replicate the modifiedU-BR1TE card 24M configuration of FIG. 4, as described above.

Embodiment 8—Modified Line Card with Smart Jack Connection to NT-1Interface FIG. 15

In an eighth embodiment of the invention, similar to the secondembodiment for extended ISDN applications, rather than employ themodified network termination interface 21M of FIG. 5 to provide theauxiliary POTS signalling path and an associated loss ofpower-responsive relay switch, these auxiliary channel-connectivityfunctions are provided through separate ‘smart’ jack module 26, asdiagrammatically shown in FIG. 15, which connects the local loop 13 froma modified line card 12M in the switch to the RJ45 jack of aconventional network termination interface 21 and is operative toprovide separate RJ11 and RJ45 connections to the auxiliary POTS phone25 and to the ISDN terminal equipment 22, respectively.

Embodiment 9—Smart Jack Connection to Unmodified Line Card Via ISDN PotsBack-up Interface FIGS. 16 and 17

In accordance with a ninth embodiment of the present invention, loss ofpower POTS back-up service is provided to the non-extended distance ISDNcommunication system diagrammatically illustrated in FIG. 16, wherein,similar to the extended distance system architecture of FIG. 6, the‘smart’ jack module 26 (shown in detail in FIG. 7, described above)connects the local loop 13 to an RJ45 jack of a conventional networktermination interface 21 and is operative to provide separate RJ11 andRJ45 connections to the auxiliary POTS phone 25 and to the ISDN terminalequipment 22, respectively. In this embodiment, in order to accommodatethe analog signalling format of the POTS phone, rather than replace theline card 12 in the central office switch 11 with a modified line card12M, an ISDN POTS back-up interface is installed in the local loop 13,as shown at 28 in FIG. 16.

As shown in detail in FIG. 17, the ISDN POTS back-up interface 28 isconfigured similar to the modified U-BR1TE card configuration of FIG. 4and includes an auxiliary digital/analog interface 750, a loop relay 720and, associated with the card's microcontroller 700, a loss of powermonitoring mechanism, which, in the event of an emergency POTS mode ofoperation, is operative to selectively control the operation of the looprelay 720, and thereby control the substitution of the auxiliarydigital/analog interface 750 in place of the normally employed ISDNtransceiver circuitry.

In the ISDN POTS back-up interface of FIG. 17, respective tip and ringleads 13T and 13R of the network side of local loop 13 are terminated byway of a network termination U transceiver interface 710, whichinterfaces 2B1Q data with the network side of local loop 13. Networktermination U transceiver interface 710 is controlled by microcontroller700 via a control link 715, and is also coupled via a first ISDN bus 705to a data router unit 730. Data router 730 is coupled via a second ISDNbus 735 to a loop termination U interface transceiver 740, whichinterfaces 2B1Q data with the customer premises side of local loop 13.The data router 730 is operative to either transparently andbidirectionally route 2B+D data between transceivers 710 and 740, orroute 1B+D data between the network U transceiver 710 and a codec 760within the auxiliary digital/analog interface 750, by way of a bus 745,during POTS back-up mode. Microcontroller 700 is coupled to looptermination U interface transceiver unit 740 via a control link 755, andto data router 730 via a control link 765. D channel data is coupledbetween microcontroller 700 and data router 730 by way of bus 775.

The auxiliary digital/analog interface 750 of the ISDN POTS back-upinterface of FIG. 17 includes codec unit 760 and a subscriber loopinterface (SLI) 770. The codec 760 and the SLI 770 are controllablyconnected in circuit between bus 745 to the data router 730 and tip andring leads 721 and 722, respectively, to first terminal contacts 731 and732 of relay 720. U transceiver interface 740 is coupled via respectivetip and ring leads 725 and 726, respectively, to second terminalcontacts 735 and 736 of relay 720. A pair of switchable arms 741 and 742of relay 720 are coupled to respective tip and ring leads 13T1 and 13R1of the customer premises side of the interface. Relay 720 has a winding727 coupled to a relay driver 728 which is controlled by microcontroller700.

SLI 770 is also coupled to each of a 10 KHz tone detector 780 and a dualtone multifrequency (DTMF) and pulse detector 790, respective outputs781 and 791 of which are coupled to microcontroller 700. The 10 KHz tonedetector 780 is employed as a wake-up tone detector and supplies anoutput signal over line 781 to the microcontroller 700, in response tothe network termination interface at the customer premises generating a10 KHz tone upon power-up. DTMF detector 790 produces signals on line791 associated with tone signals (such as dial tones) sourced from thecustomer premises equipment 22.

As in the modified U-BR1TE card configuration of FIG. 4, describedpreviously, the control software employed by microcontroller 700monitors the local loop leads 13T1, 13R1 to the network terminationinterface 21, in order to determine the ability of the networktermination interface to provide normal telephone service with thecustomer's data terminal equipment (DTE) 22. For this purpose,microcontroller 700 employs a loss of power monitoring mechanism, whichmonitors the signalling condition on the tip and ring pair 13T1, 13R1via U-transceiver unit 740, by looking for a signalling conditionrepresentative of loss of power to the network termination interface, asdescribed above.

In response to detecting a loss of power condition, microcontroller 700generates a switch control output signal on line 729 to relay driver728, so as to operate relay 720 and thereby cause the tip and ring leads13T1 and 13R1 of the customer premises side of the local loop to bedecoupled from contacts 735 and 736 and the tip and ring path for normalISDN signal processing to U-transceiver unit 740 and, instead, couplesthe local loop leads 13T1 and 13R1 to contacts 731 and 732 to auxiliarytip and ring leads 721 and 722 to digital/analog interface 750.

When placed in this POTS back-up mode, control signals (pulse or tonedialing signals) from the customer's POTS phone 25 are output asstandard (Q921/931) messages over D channel link 775 frommicrocontroller 700 to the data router 730 for application to the Dchannel portion of bus 705 and transmission on the network side of thelocal loop by way of U transceiver 710. Digital/analog interface 750converts sampled analog voice signals received from the POTS telephone25 into 64 Kbps digitally formatted voice signals, that are coupled overISDN bus 745 to data router 730 for application via a B channel portionof the ISDN communication bus 705 of U transceiver interface 710 andtransmission therefrom as 2B1Q data over the network side of the localloop 13 to the line card in the central office.

In the receive direction from the network side of the local loop 13,incoming 2B1Q signals from the line card 12 are converted by transceiver710 into 2B+D signals and applied via ISDN bus 705 to data router 730.The data router couples the bearer (B) channel (coded voice) data overlink 745 from transceiver 710 to auxiliary digital/analog interface 750,which regenerates outgoing analog voice signals for application overtip/ring pair leads 721, 722 through relay 720 to the tip and ring leads13T1 and 13R1 of the customer premises side of the local loop.

Similar to the operation of the modified U-BR1TE card architecture ofFIG. 4, described above, in response to power being restored to thecustomer premises equipment (corresponding to a signalling recoverycondition), where the network termination interface is designed togenerate a 10 KHz tone on power-up, a signal is coupled over line 781from 10 KHz tone detector 780 to microcontroller 700, indicating thatthe POTS phone 25 is not in use (OFF-HOOK). (If the POTS phone 25 iscurrently OFF-HOOK, the call is allowed to be completed.)Microcontroller 700 then deactivates relay 720, decoupling the customerpremises side of the local loop 13 from auxiliary digital/analoginterface 750, and recoupling leads 13T1 and 13R1 to loop termination Utransceiver 740.

Where the network termination interface is of the type that does nottransmit a 10 KHz tone on power-up, microcontroller 700 may periodicallydeactivate relay 720 and thereby repeatedly decouple auxiliarydigital/analog interface 750 from the local loop, and then recouple thelocal loop to transceiver interface 740. During each of these periodicchange-overs, U transceiver interface 740 attempts to reestablishdigital communication capability over the local loop with the networktermination interface 21. If it is unable to do so within a prescribedperiod of time, microcontroller 700 again switches the relay 720 back tothe POTS mode configuration, and thereby returns the connection betweenthe customer premises side of the local loop and the auxiliarydigital/analog interface 750, so as to decouple the local loop from theU transceiver interface 740.

Embodiment 10—Integrated ISDN Phone having Pots Back-up Connection toUnmodified Line Card Via ISDN Pots Back-up Interface FIG. 18

In accordance with a tenth embodiment of the present invention, loss ofpower POTS back-up service is provided to the non-extended distance ISDNcommunication system diagrammatically illustrated in FIG. 18, wherein,similar to the extended distance system architecture of FIG. 8, thenetwork termination interface 21 at the customer premises site isreplaced with the integrated ISDN telephone and network terminationinterface unit 22M, which includes a POTS phone back-up, shown in detailin FIG. 9. As in the ninth embodiment of FIGS. 8 and 9, in order toaccommodate the analog signalling format of the POTS phone, rather thanreplace the line card 12 in the central office switch 11 with a modifiedline card 12M, the ISDN POTS back-up interface 28 of FIG. 9 is installedin the local loop 13.

Embodiment 11—Integrated ISDN Terminal Adapter with Pots Connection toUnmodified Line Card Via ISDN Pots Back-up Interface FIG. 19

Pursuant to an eleventh embodiment of the invention, diagrammaticallyillustrated in FIG. 19, the modified network termination interface NT-121 of the non-extended distance system of FIG. 2 is replaced by theintegrated ISDN terminal adapter and network termination interface 24M2,shown in detail in FIG. 11, described above. In addition, as in theninth and tenth embodiments, in order to accommodate the analogsignalling format of the POTS phone, rather than replace the line card12 in the central office switch 11 with a modified line card 12M, theISDN POTS back-up interface 28 of FIG. 9 is installed in the local loop13 between the line card 12 and the integrated ISDN terminal adapter andnetwork termination interface 24M2.

Embodiment 12—Modified NT1 Interface with Pots Back-up Connection toUnmodified Line Card Via ISDN Pots Back-up Interface FIG. 20

Pursuant to a twelfth embodiment of the present invention,diagrammatically illustrated in FIG. 20, POTS back-up service isprovided to a non-extended distance ISDN communication system, whereinthe network termination interface NT-1 21 of the non-extended distancesystem of FIG. 2 is replaced by the modified network terminationinterface NT-1 24M, shown in detail in FIG. 5, described above. Inaddition, as in the ninth through eleventh embodiments, in order tomaintain integrity of the ISDN communication path (local loop) betweenthe network termination interface and the central office switch, for theanalog signalling format of the POTS phone, rather than replace the linecard 12 in the central office switch 11 with a modified line card 12M,the ISDN POTS back-up interface 28 of FIG. 9 is installed in the localloop 13 between the line card 12 and the integrated ISDN terminaladapter and network termination interface 21M2.

Embodiment 13—Integrated ISDN Terminal Adapter with ISDN S/T Interfaceand Pots Back-up Connection to Unmodified Line Card Via ISDN Pots PortFIGS. 21 and 22

Pursuant to a thirteenth embodiment of the invention, diagrammaticallyillustrated in FIGS. 21 and 22, in the embodiment of FIG. 19, theintegrated ISDN terminal adapter and network termination interface 21M2,shown in detail in FIG. 11, described above is replaced by the modifiedconfiguration 24M3 shown in FIG. 22, to provide for connection to anISDN S/T interface port. As shown therein, rather than having aconnection for customer interface data to data terminal equipment 22,processor 630 is coupled to an S/T interface 650, which interfaces a2B+D channel with the U-interface 620 and is coupled to via S/T port toan ISDN terminal equipment, terminal adapter 22A. The D channel iscoupled between the processor 630 and the U-interface 620, while the Bchannel is coupled between the U-interface 620 and the SLI and codec640.

As will be appreciated from the foregoing description, the need toensure continuous telephone service to a customer premises served by anISDN line, without requiring that the customer maintain an additionalPOTS line as an emergency back-up to the normally used ISDN service, issuccessfully addressed by a modification of conventional ISDN signallingcircuits and network termination interface components, together with anaugmentation of the communication control software employed therein, sothat, in the event of a loss of power to customer premises equipment, acommunication link between an auxiliary POTS telephone and an ISDNcommunication path to the central office may be established. There neednot be any modification of the central office switch, per se, so thatthe integrity of the ISDN communication path with the central officeline card remains unaffected. As a result, the central office equipmentcan continue to conduct standard ISDN communications with the customerpremises equipment, even though the customer is employing a POTS back-upanalog phone.

While we have shown and described a plurality of embodiments of thepresent invention, it is to be understood that the same is not limitedthereto but is susceptible to numerous changes and modifications asknown to a person skilled in the art. For example, it should be realizedthat in addition to its use with ISDN switching equipment, such as, butnot limited to, the above mentioned an AT&T central office 5ESS switch,a DMS100 switch, manufactured by Northern Telecom, etc. In addition, thetransmission equipment may be of various types, such as, but not limitedto digital multiplexers, D4 channel banks, SLC 96 cards, SKC 5 units,etc. Consequently, we do not wish to be limited to the details shown anddescribed herein but intend to cover all such changes and modificationsas are obvious to one of ordinary skill in the art.

What is claimed:
 1. A method of providing auxiliary plain old telephoneservice (POTS) capability between an auxiliary POTS telephone at acustomer premises, and a communication link coupled to a digitalcommunication interface serving digital communication equipment, whichis installed at said customer premises and is powered exclusively ofsaid communication link, in the event that said digital communicationequipment is unable to provide telephone service, said method comprisingthe steps of: (a) decoupling said communication link from a normaldigital signaling path through said digital communication interface tosaid digital communication equipment and, instead, coupling saidcommunication link to an auxiliary digital/analog signaling path, whichis operative to convert outgoing analog signals from said auxiliary POTStelephone to digital communication signals for transmission over saidcommunication link, and to convert incoming digital communicationsignals from said communication link into analog signals for saidauxiliary POTS telephone; and (b) coupling said auxiliary POTS telephoneto said auxiliary digital/analog signaling path.
 2. A method accordingto claim 1, wherein said event that said digital communication equipmentis unable to provide telephone service corresponds to a loss of powerfor operating said digital communication equipment.
 3. A methodaccording to claim 2, wherein step (a) further comprises monitoringstatus information signals associated with the power status of saiddigital communication equipment and, in response to said statusinformation signals being indicative of loss of power to said digitalcommunication equipment, decoupling said communication link from saidnormal digital signalling path and, instead, coupling said communicationlink to said auxiliary digital/analog signaling path.
 4. A methodaccording to claim 1, wherein step (a) further comprises detecting lossof synchronization of digital signals from said digital communicationequipment and, in response to detecting said loss of synchronization ofdigital signals, decoupling said communication link from said normaldigital signalling path and, instead, coupling said communication linkto said auxiliary digital/analog signaling path.
 5. A method accordingto claim 1, further including the step (c) of monitoring saidcommunication link for a signaling recovery condition representative ofthe ability of said digital communication equipment to provide normaltelephone service and, in response to detecting said signalling recoverycondition, decoupling said communication link from said auxiliarydigital/analog signaling path, and recoupling said communication link tosaid normal digital signaling path through said digital communicationinterface to said digital communication equipment.
 6. A method accordingto claim 5, wherein step (c) comprises monitoring said communicationlink for a prescribed tone signal and, in response to detecting saidprescribed tone signal, decoupling said communication link from saidauxiliary digital/analog signaling path, and recoupling saidcommunication link to said normal digital signalling path through saiddigital communication interface.
 7. A method according to claim 5,wherein step (c) comprises decoupling said communication link from saidauxiliary digital/analog signaling path, recoupling said communicationlink to said normal digital signalling path through said digitalcommunication interface, and attempting to reestablish digitalcommunication capability with said digital communication equipment viasaid communication link.
 8. A method according to claim 7, wherein step(c) further comprises, in response to not being able to reestablishdigital communication capability with said digital communicationequipment at said customer premises via said communication link within aprescribed period of time, recoupling said communication link to saidauxiliary digital/analog signaling path, and decoupling saidcommunication link from said normal digital signalling path.
 9. A methodaccording to claim 7, wherein step (c) is carried out periodically todetermine whether normal telephone service capability has been restoredto said digital communication equipment at said customer premises. 10.An apparatus for providing auxiliary plain old telephone service (POTS)capability between an auxiliary POTS telephone at a customer premises,and a communication link coupled to a communication interface servingdigital communication equipment, which is installed at said customerpremises and is powered exclusively of said communication link, in theevent that said digital communication equipment is unable to providetelephone service, comprising: a digital signaling path through saidcommunication interface between said communication link and said digitalcommunication equipment; an auxiliary digital/analog signaling paththrough said communication interface between said communication link andsaid digital communication equipment, and being operative to convertoutgoing analog signals from said auxiliary POTS telephone to digitalcommunication signals for transmission over said communication link, andto convert incoming digital communication signals from saidcommunication link into analog signals for said auxiliary POTStelephone; and a communication path controller, which is operative, inresponse to said digital communication equipment being unable to providetelephone service, to couple said auxiliary digital/analog signalingpath to said communication link and said auxiliary POTS telephone. 11.An apparatus according to claim 10, wherein said communication pathcontroller is operative, in response to a loss of power for operatingsaid digital communication equipment, to couple said auxiliarydigital/analog signaling path to said communication link and saidauxiliary POTS telephone.
 12. An apparatus according to claim 10,wherein said communication path controller is operative, in response todetecting loss of synchronization of digital signals from said digitalcommunications equipment, to decouple said communication link from saidnormal digital signalling path and, instead, to couple saidcommunication link to said auxiliary digital/analog signaling path. 13.An apparatus according to claim 10, wherein said communication pathcontroller is operative to monitor said communication link for asignaling recovery condition representative of the ability of saiddigital communications equipment to provide normal telephone serviceand, in response thereto, to decouple said communication link from saidauxiliary digital/analog signaling path, and to recouple saidcommunication link to said normal digital signalling path through saiddigital communications interface to said digital communicationsequipment.
 14. An apparatus according to claim 10, wherein saidauxiliary digital/analog interface contains a codec and a subscriberloop interface circuit, which are controllably connected in circuitbetween a digital subscriber loop to said customer premises and saidcommunication link to a central office.
 15. An apparatus according toclaim 10, wherein said communication link comprises an extended distancecommunication link from a line card for a central office switch, andwherein said auxiliary digital/analog interface and said communicationpath controller are located at said customer premises.
 16. An apparatusaccording to claim 10, wherein said communication path controllerincludes a loss of power-responsive circuit, which is normally poweredby a power source for operating said digital communication equipment atsaid customer premises and is operative, in response to a loss of powerfor said digital communication equipment, to couple said auxiliary POTStelephone to said digital subscriber loop.
 17. An apparatus according toclaim 16, wherein said communication path controller includes a hybridunit which integrates said auxiliary POTS telephone with said digitalcommunication equipment, such that said digital communication equipmentis normally coupled to said digital subscriber loop, but in response tosaid loss of power for said digital communication equipment, isoperative to couple said auxiliary POTS telephone to said digitalsubscriber loop.
 18. An apparatus according to claim 10, wherein saidcommunication link extends over a local digital subscriber loop from aline card for a central office switch, and wherein said auxiliarydigital/analog interface and said communication path controller includecircuitry located within a transceiver in said line card.
 19. Anapparatus according to claim 10, wherein said communication link extendsover a local digital subscriber loop from a line card for a centraloffice switch, and said auxiliary digital/analog interface and saidcommunication path controller includes circuitry contained within atransmission equipment transceiver unit in said line card, and wherein aloss of power-responsive circuit is located at said customer premises,and is operative, in response to a loss of power to said digitalcommunication equipment, to couple said auxiliary POTS telephone to saiddigital subscriber loop.